Magnetic Field Sensor With Shared Electrodes For Offset Error Reduction
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Solution Overview
Problem
Existing magnetic field sensors face challenges with offset errors and sensitivity to misalignment, particularly in detecting angular positions of magnetic fields, due to small differential signals and mechanical contact issues.
Innovation Solution
A magnetic field sensor structure featuring a ring-shaped well with inner and outer electrodes arranged at equidistant angular positions, along with a biasing-and-readout circuit that selectively applies bias currents and reads differential Hall voltages to determine the angular position of a magnetic field, reducing sensitivity to offset errors and misalignment through correlated sampling and modulated readout techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional horizontal or vertical Hall elements are used, then the sensor can detect magnetic field components, but the small differential signal (100 microVolts to 1 milliVolt) requires amplification and is sensitive to offset errors
Solution Approach 1:
The sensor is divided into multiple independent Hall elements (first, second, third, and fourth Hall elements) arranged in a specific geometric pattern. Each element contributes to the overall measurement, allowing the system to detect magnetic field components while canceling out offset errors through differential measurement between multiple elements.
Solution Approach 2:
A magnetic concentrator is introduced as an intermediary component between the magnetic field source and the Hall elements. This concentrator enhances the magnetic field signal at the sensor location, improving the signal-to-noise ratio and reducing the impact of offset errors by amplifying the useful signal relative to the background offset.
2Measurement precision
If the sensor structure uses multiple electrodes and complex biasing circuits, then offset error compensation is improved, but the device complexity increases
Solution Approach 1:
The biasing circuit is designed to serve multiple functions simultaneously: it provides bias currents to multiple Hall elements, enables sequential operation modes (first mode and second mode), and facilitates offset error compensation through differential measurement. This multi-functionality reduces the need for separate dedicated circuits for each function.
Solution Approach 2:
The sensor operates in periodic cycles, alternating between a first mode and a second mode. In each cycle, bias currents are sequentially applied to different combinations of Hall elements, allowing offset errors to be measured and compensated during specific phases while maintaining continuous magnetic field detection capability.
3Measurement precision
If mechanical contact is used between rotor magnet and stator sensor, then angle measurement can be performed, but wear and mechanical contact issues reduce reliability under harsh conditions
Solution Approach 1:
The mechanical contact-based angle measurement system is replaced with a contactless magnetic field sensing system. Hall elements detect the magnetic field generated by a rotor magnet without physical contact, eliminating wear and mechanical friction while maintaining angular position measurement capability. This substitution enables hermetic encapsulation and operation under harsh environmental conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a robust and accurate method for determining angular positions with reduced sensitivity to offset errors and external fields, enhancing the reliability and precision of magnetic field sensing.
Implementation Method 1
a differential Hall voltage being indicative of the relative magnitude of a magnetic field component Bz perpendicular to the plane of the Hall element
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
A magnetic field sensor structure (1) having a number (N) of inner, outer and intermediate electrodes (5, 4, 6), arranged in a particular manner, such that groups of four electrodes can be used to form horizontal Hall elements (9), whereby neighboring Hall elements "share" one of the two readout electrodes. Multiple Hall elements may be biased and readout simultaneously. A modulated or unmodulated readout-technique may be used. Integrated magnetic concentrator (IMC) may be added to the structure (1). The number of Hall elements may be odd or even. The structure (1) can be used e.g. to measure the magnetic field of a 2-pole, 4-pole or 6-pole ring or disk magnet (2).